On a magneto-optical disk, a thin magnetic film having vertical magnetic anisotoropy is usually used as a recording medium, and a laser beam which is converged to a spot of substantial 1 .mu.m is applied thereto in order to perform recording, reproducing and erasing operations. More concretely, the recording and erasing operations are achieved by effecting magnetization reversal by an external magnetic field by utilizing the fact that coercive force becomes lowered due to a temperature rise in the spot where the laser beam is focused. On the other hand, the reproducing operation is achieved by utilizing the fact that a plane of polarization of the laser beam rotates by magneto-optical effect and detecting a rotation of the polarizing plane by an analyzer.
An arrangement has been suggested wherein each track of the magneto-optical disk is divided into a plurality of sectors in the circumferential direction, and in the leading area of each sector, a pre-format part is disposed, wherein a sector mark, address information and other data are preformed in pits, while recording, reproducing and erasing operations of magneto-optical signals are performed in the other area of each sector as a recording area for magneto-optical signals by every sector unit. In that case, it is necessary to provide timing control so that recording, reproducing and erasing operations can be performed in the recording area for magneto-optical signals except the pre-format part.
In FIG. 21, there is illustrated a conventional information recording and reproducing device for performing recording and reproducing operations on and from a magneto-optical disk by the use of the above-mentioned method. A reproduced signal A is released from an information reproducing circuit 1, and the reproduced signal A is inputted to a synchronization detection circuit 2. In the synchronization detection circuit 2, synchronization detection for each sector is performed from, for example, a signal of a sector mark which is a part of the reproduced signal A.
A synchronization detection signal B released from the synchronization detection circuit 2 is inputted to a timing control circuit 3, where timing control is provided according to the synchronization detection signal B, and consequently, a reproducing timing signal C is sent to the information reproducing circuit 1 during a reproducing operation, while a recording/erasing timing signal E is sent to an information recording/erasing circuit 4 during a recording or erasing operation. With the above arrangement, recording, reproducing and erasing operations are performed in the recording area for magneto-optical signals of each sector. Additionally, the synchronization detection by the synchronization detection circuit 2 is performed separately from the reproducing operation of information so as not to disturb the synchronization detection due to the reproducing timing signal C.
However, in the device shown in FIG. 21, since the timing control is provided only by the use of the synchronization detection, there sometimes arises a situation wherein an error occurs in synchronization detection or time lag in detection occurs in the synchronization detection circuit 2, and consequently an accurate timing control cannot be executed. More specifically, errors in the timing control arise because reed gate signals of a PLL (Phase Locked Loop) included in the information reproducing circuit 1 become inaccurate, pulling-in operation cannot be performed, or the runout of the locked loop is apt to occur. Accordingly, the conventional method has a problem in that reliability of recording, reproducing and erasing operations cannot be fully achieved. Further, when an error occurs in synchronization detection, timing control of AGC (Automatic Gain Control) is adversely affected.